Grooming our body hair can be comparable to landscaping. We tweeze our eyebrows, trim our beards, and shave our legs to strip away thousands of unwanted hairs. In the process, we come across an unsightly view — butt hair. While we’re aware it exists around our anus, we wonder, "does it serve a purpose?"
In Sci Show's video, "Why Do We Have Butt Hair?" host Hank Green explains no one actually knows why we have butt hair, but (no pun intended) it may simply exist because there's "no significant evolutionary pressure against it." In other words, it does not get in the way of humans procreating. It may just be a side effect of unintelligent design.
Other theories suggest butt hair facilitates scent communication. Throughout human evolution, communication through scent has played a pungent role. This is why we have body hair in the same areas where we produce odors. The hair is there to hold onto sebaceous, or oily, secretions that have their own smell and are consumed by bacteria that produces even more smells.
Since we all have different smell compounds, and our own microbiomes, each of us smells differently. It is presumed our early human ancestors used their personal smell to help them with everything from broadcasting territorial rights to attracting mates. Butt hair may simply be another way our ancestors enhanced their smell profiles.
Lastly, friction may explain the evolutionary purpose of butt hair. Skin rubbing on skin causes friction, which can lead to irritation, rashes, and even infection. Hairs may act as a bit of a protective layer, and those sebaceous secretions hair helps spread work to reduce the pain of chafing. Butt hair could act like a natural anti-chafing cream.
It's important to remember there hasn't been much research done to verify these theories, and "not every bit of our physiology needs an evolutionary purpose."